A tectonic lake formed by the northern Anatolian Fault line to the east of the Marmara Region. Located at the foot of the Samanli Mountains, most of the lake is located in Sakarya and the western side is located in Kocaeli province. Once part of the Sea of Marmara, the lake left the sea and became a freshwater lake alone, becoming the lifeblood of the region.
The length of the lake is about 16 kilometers and the area is 42 square kilometers. Its deepest point is 61 meters, with an average depth of about 30 meters. The majority of the main sources of nutrition come from the Samanli Mountains, located south of the lake. The main streams that feed Sapanca are Esme Creek, Goat Creek, Istanbul Creek, Burnt Creek, Derbent Creek, Double Pinar Creek, Stallion Creek, Arifiye Creek and Mineral Creek. These are the lifeblood of both the lake and the forests in the region. Lake Sapanca is also an important wetland where tens of thousands of migratory birds stay every year. Studies show the presence of around 80 bird species. The lake is an important wintering area for apple head patka and Hungarian duck. The most most found bird species in the lake is clumsy. The fact that this bird is hunted in piles is damaging the lake. Because the decrease in clumsy mechanes causes the plants to spread rapidly over the lake, which they prevent from growing by eating. Springs, carp and pike are common in the lake.
Surfing, rowing, sailing and sea biking are sports that can be done on the lake. It is also possible to swim in certain places. Although Lake Sapanca is surrounded by settlements, it has so far not been affected by pollution as much as other lakes due to its strong nutritional resources. However, traces of pollution are found, albeit on the ground.